Diagnosis. This and Arctornis meridionalis
Holloway comb. n. have similar facies: the angled hindwings and
the subapical translucent patches of the pale-brown suffused forewings
distinguish them from other Arctornis. The species differ in size and
male genitalia: obtusa is larger, with the valve harpe longer and with a
diagnostic central bulge.

Taxonomic note. These two species belong to the Cassidia group, reviewed by
Holloway (1982b). There is a moderate areole in the forewing venation.

Geographical range. Borneo, Sulawesi.

Habitat preference. The species occurs frequently in a wide range of
lowland forest types, and much more rarely at altitude, the highest record being
from 1930m on G. Kinabalu.